curl --request POST \
  --url http://localhost:3000/v1/inventory/convert \
  --header 'Content-Type: application/json' \
  --data '
{
  "parent_sellable_product_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "child_sellable_product_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "parent_quantity": 1,
  "child_inventory_group_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a"
}
'

{
  "success": true,
  "parent_quantity_converted": 123,
  "child_quantity_created": 123,
  "child_inventory_item": "<unknown>"
}